Process to recover raw rubber compound from semi-finished, reinforced, technical rubber products, especially hoses, before cross-linking, and equipment therefor

ABSTRACT

A process for recovering raw rubber compounds from unvulcanized reinforced, semi-finished technical rubber products includes pressing the rubber products between metal surfaces heated to a temperature from 50 to 300° C., or preheating the rubber products to a temperature from 50 to 300° C.; and then pressing the rubber products between metal surfaces. Also, equipment for carrying the above process including a preheated or forewarmed space, and rolls in close proximity to the preheated space, the rolls rotating preferably at the same speed, but in opposite directions. The equipment has means for the adjustment of the gap between the rolls, drive means for the rolls, and if required, may be equipped with known aligning, guiding and forwarding mechanisms.

FIELD OF THE INVENTION

The present invention relates to the recovery of raw rubber compoundsused for recycling and/or reprocessing, from the extruded faultyproducts or waste (scrap), which are produced during the manufacture ofreinforced rubber hoses or tubes for the automotive and otherindustries, and more particularly to a process for recovering raw rubbercompound from semi-finished, reinforcement containing technical rubberproducts, especially hoses (tubes), before crosslinking (vulcanizing)the same. The invention also relates to equipment for implementing thisprocess.

BACKGROUND OF THE INVENTION

Recently, unvulcanized, raw rubber compounds have been recycled fromscrap, produced during extrusion or calandering, only if the scrap doesnot contain any reinforcement. Scrap raw rubber containing reinforcementis not suitable for further processing (by extrusion or calandering,also known as procuring), because the rubber compound becomeselasticized and bonds to the reinforcement due to heat transfer duringthe procuring process.

Currently, there are no known methods for recovering unvulcanized rubberscrap formed during the manufacturing process, although there areseveral known methods for recovering rubber from vulcanisedend-products. Manufacturers usually recycle the unvulcanized rubberafter milling it in ripped two roll mills or cutting it in shreddersinto particles having an average particle size of smaller than 10 mm.

The resulting material can be used for the production of technicalrubber products, rubber sheets and solid rubber tires, as secondary rawmaterial having a high (42-45%) rubber content (see Gumiipari Kezikonyv,2^(nd) Volume, TAURUS-OMIKK, Budapest, 1989).

It should be understood, that the above methods can not be used forproducing reinforced, straight or specially shaped rubber hoses (used inthe automotive industry for water and oil hydraulic and gas hoses),since the recovered material can not be admixed with the new raw rubbercompound used in manufacturing hoses. The use of such textile containingraw material is not acceptable, because the working conditions of theproduct the stresses on the product, further the manufacturingrequirements do not allow it.

Therefore, recycling of reinforced rubber from the scrap produced duringor before procuring has not been possible.

The above technical problem results in unnecessary raw material,transport and waste disposal costs for manufacturers, and it alsocreates environmental problems, as produced scrap is not practicallybiodegradable, and thus, pollutes the environment.

Furthermore, during manufacturing of such rubber products, the estimatedamount of reinforcement containing scrap or waste produced during theextrusion (calandering) step, is about 2-15% of the weight of theend-product. Therefore, there is a great need for a process whichrecovers recyclable raw rubber compound from unvulcanized, reinforcedrubber scrap.

A process has been disclosed in DE 3137502 for recycling of vulcanizedand unvulcanized rubber scrap. According to this process, the compoundscontaining such materials are exposed to heat in boiling hydrocarbonsolvents, under pressure and under inert atmosphere. The productobtained by this process can be used as plasticizing agent or demulcentfor rubber compounds. However, this process is not suitable forrecovering recyclable raw rubber compound from unvulcanized, reinforcedrubber scrap.

Accordingly, the aim of the present invention is to provide a method forrecovering raw rubber compound from unvulcanized, reinforced rubbercompounds.

SUMMARY OF THE INVENTION

The present invention involves a process for recovering raw rubbercompounds from unvulcanized reinforced, semi-finished technical rubberproducts. In one embodiment of the invention the process comprisespressing the rubber products between metal surfaces heated to atemperature from 50 to 300° C., thereby causing elasticized rubber toflow out; and cooling the elasticized rubber to ambient temperature.

In another embodiment of the invention the process comprises preheatingthe rubber products to a temperature from 50 to 300° C.; pressing therubber products between metal surfaces, thereby causing elasticizedrubber to flow out; and cooling the elasticized rubber to ambienttemperature.

The present invention also involves equipment for carrying the aboveprocess. The equipment comprises a preheated or forewarmed space, androlls in close proximity to the preheated space, the rolls rotatingpreferably at the same speed, but in opposite directions. The equipmenthas means for the adjustment of the gap between the rolls, drive meansfor the rolls, and if required, may be equipped with known aligning,guiding and forwarding means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a preheating unit; and

FIGS 2A and 2B show a forewarming unit.

DETAILED DESCRIPTION OF THE INVENTION

In order to better understand the invention, the same has been disclosedin connection with (rubber hoses), however it should be clear that aperson skilled in the art, will be able to apply the present inventionfor rubber belts or other technical rubber products as well, on basis ofthe teaching of the present specification.

In the present invention, it has been surprisingly found that the rubbercompound becomes elasticized, and flows out from the space between thereinforcements, when the unvulcanized, reinforced rubber semi-product isplaced between metal surfaces, which are heated to a predeterminedtemperature; or when the rubber semi-product is preheated to a certaintemperature and then placed between metal surfaces, by which a certainpressure is applied. The rubber compound can then be separated from thereinforcements, even manually. The recovered rubber is cooled to roomtemperature and recycled.

It is known in the art, that rubber hoses are manufactured in thefollowing technological steps: a) extrusion: b)vulcanization; and c)finishing. During the extrusion step (which known as calandering in caseof rubber belts), a non-reinforced rubber hose (seal) is produced by anextruder. The hose possesses the required properties, and forms an innerliner. Reinforcement is laid on the inner liner with a braider orspiralling machine, and a cover layer is put on the reinforced innerliner with a cross headed extruder. The hose is then cut to a requiredlength by a cutting machine.

During the vulcanizing step, the semi-finished hoses cut to the requiredlength are placed on a mandrel having the required shape, and then thehoses are vulcanized under selected operational conditions, such asoptimal temperature, pressure, vulcanising time, humidity, etc.

During the finishing step, the hoses are pulled off from the mandrelafter vulcanization, and then inspected, repaired, labelled and packed.

The process according to the present invention enables the manufacturerto recover and to make the rubber compound recyclable from thereinforced rubber scrap produced during the adjustment or routineoperation of extrusion or calandering.

The essence of the process of the present invention is that thereinforced unvulcanized semi-finished rubber products, preferably rubberhoses, are pressed between metal surfaces heated up to a temperature of50-300° C.; or are pressed by other means; or the rubber products arepreheated to the above mentioned temperature and placed between metalsurfaces and pressed. The elasticized rubber compound flowing out isrecovered and cooled to ambient temperature.

According to an embodiment of the process of the present invention, thereinforced unvulcanized semi-finished rubber hose is placed betweenpressing plates (in other words between metal surfaces), which areheated to the above mentioned temperature, and are pressed with 5-50 tonforce.

According to a further embodiment of the process of the presentinvention, the reinforced, unvulcanized, semi-finished rubber hoses arecut into 20-80 cm long pieces, and preheated in a preheating unit for0.5-10 minutes. The cut, and preheated pieces are led between a pair ofrotating rolls, which are preferably rotating at the same speed, but inopposite directions.

A further embodiment of the process according to the present inventionis to preheat the reinforced, unvulcanized, semi-finished rubber hosesto a temperature of 50-300° C., preferably between 50-160° C. Theheated, moving pressing plate may be moved by a mechanical or ahydraulic system.

In the case of using a preheating unit, the reinforced, unvulcanized,semi-finished rubber hoses cut to a required length, are preheated to40-300° C., preferably to a maximum of 160° C., for 0.5-10 minutes. Thepreheated, reinforced, unvulcanized, semi-finished rubber hoses are ledbetween a pair of rotating rolls, which are rotating preferably at thesame speed, but in opposite directions. The gap between the rolls can beadjusted between 0.5-50 mm with a screw shaft, depending on the diameterof the rubber hoses. The rotating rolls are driven by a heavy-dutyelectric motor with a cogwheel transmission. The free length of therolls is a minimum of 250 mm.

In the case of using a preheating unit, the preheating unit's length isselected between 300-1000 mm and its temperature is selected from theabove mentioned range. The reinforced unvulcanized, semi-finished rubberhoses go through the preheating unit, and then are led between the rollsrotating in the opposite directions. The rolls are placed directly afterthe preheating unit. The gap between the rolls can be adjusted in thesame way and in the same range as described above, and also the freelength of the rolls is the same as given above.

The temperature and time of preheating is selected taking into accountthe vulcanization parameters of the material to be processed.

The process is carried out similarly in case of using conical rolls, toenhance the efficacy of the process.

The following example is to illustrate the process of the invention, forbetter understanding. It should be noted however, that the process ofthe invention is not restricted to this example.

EXAMPLE

An unvulcanized semi-finished rubber hose, containing polyamidereinforcements and having 25 mm outer diameter, 2 mm outer wallthickness and 2 mm inner wall thickness, is pressed between pressingplates preheated to 160° C. for 3 seconds with 40 ton force. Aftercooling to ambient temperature, the rubber compound is obtained. About70-80% of the rubber compound is recovered in this way.

The equipment according to the invention to carry out the process of theinvention is characterised in that it contains a preheated or forewarmedspace, and rolls in close proximity to the preheated space (e.g. beforeor beside it), the rolls rotating preferable at the same speed, but inopposite directions. The device has means for the adjustment of the gapbetween the rolls, drive means for the rolls, and if required, may beequipped with known aligning, guiding and forwarding means.

FIGS. 1A and 1B show a preheating unit 1, and a reinforced,unvulcanized, semi-finished rubber hose 3. FIGS. 2A and 2B show aforewarming unit 4, and other elements, identical to those shown inFIGS. 1A and 1B. In the embodiment shown in FIGS. 1A and 1B, thepreheating unit 1 is intended for batch processing the reinforced,unvulcanized, semi-finished rubber hose 3, since the product is notnecessarily fed continuously between rolls 2, which rotate at the samespeed, but in opposite directions. On the other hand, the forewarmingunit 4 shown in the embodiment of FIGS. 2A and 2B continuously feeds thereinforced unvulcanized, semifinished rubber hose 3 between the rolls 2rotating at the same speed, but in opposite directions.

What is claimed is:
 1. A process for recovering raw rubber compoundsfrom unvulcanized reinforced, semi-finished technical rubber products,comprising: providing unvulcanized reinforced, semi-finished technicalrubber products; pressing the rubber products between metal surfacesheated to a temperature from 50 to 300° C., thereby causing elasticizedrubber to flow out; cooling the elasticized rubber to ambienttemperature.
 2. The process of claim 1, wherein pressing is performed bya pair of rolls rotating in opposite directions.
 3. The process of claim2, wherein the rolls rotate at the same speed.
 4. The process of claim2, wherein each of the rolls has a conical shape.
 5. A process forrecovering raw rubber compounds from unvulcanized reinforced,semi-finished technical rubber products, comprising: providingunvulcanized reinforced, semi-finished technical rubber products;cutting the rubber products into 20-80 cm long pieces; preheating therubber products in a preheating unit for 0.5 to 10 minutes to atemperature of 40 to 300° C.
 6. The process of claim 5, wherein therolls rotate at the same speed.
 7. The process of claim 5, wherein eachof the rolls has a conical shape.
 8. A process for recovering raw rubbercompounds from unvulcanized reinforced, semi-finished technical rubberproducts, comprising: providing unvulcanized reinforced, semi-finishedtechnical rubber products; cutting the rubber products into 20-80 cmlong pieces; preheating the rubber products in a preheating unit for 0.5to 10 minutes to a temperature of 40 to 160° C.; pressing the rubberproducts between metal surfaces defined by a pair of rolls rotating inopposite directions, thereby causing elasticized rubber to flow out; andcooling the elasticized rubber to ambient temperature.
 9. The process ofclaim 8, wherein the rolls rotate at the same speed.
 10. The process ofclaim 8, wherein each of the rolls has a conical shape.
 11. A processfor recovering raw rubber compounds from unvulcanized reinforced,semi-finished technical rubber products, comprising: providingunvulcanized reinforced, semi-finished technical rubber products;preheating the rubber products in a preheating unit to a temperaturefrom 50 to 300C.; pressing the rubber products between metal surfaces ofa pair of rolls rotating in opposite directions at the same speed,thereby causing elasticized rubber to flow out; and cooling theelasticized rubber to ambient temperature.
 12. A process for recoveringraw rubber compounds from unvulcanized reinforced, semi-finishedtechnical rubber products, comprising: providing unvulcanizedreinforced, semi-finished technical rubber products; preheating therubber products in a preheating unit for 0.5 to 10 minutes to atemperature of 50 to 160° C.; pressing the rubber products between metalsurfaces defined by a pair of rolls rotating in opposite directions,thereby causing elasticized rubber to flow out; and cooling theelasticized rubber to ambient temperature.
 13. The process of claim 12,wherein the rolls rotate at the same speed.
 14. The process of claim 12,wherein each of the rolls has a conical shape.